<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>JS阻塞</title>
    <style>
        #container{
            width: 100px;
            height: 100px;
            background: yellowgreen;
        }
    </style>
   
</head>
<body>
    <div id="container"></div>
    <script src="demo.js" defer>

    </script>
    <style>
        #container{
            border-color: blue;
        }
    </style>
</body>
</html>